1. Field of the Invention
The present invention relates to a manually operable device for displacing movable stages or the like member on a microscope, particularly to a manually operable device of the type including a couple adjusting unit for varying an intensity of couple for an operating handle as required.
2. Related Background Art
As a manually operable device of this type, there have been heretofore known those as disclosed in, for instance, an official gazette of Japanese Utility Model Publication No. 11048/1981 and an official gazette of Japanese Utility Model Publication No. 45365/1980. A device as disclosed in the former official gazette includes a pinion shaft rotatably supported on a stationary shaft, a pinion provided on one end of the pinion shaft to mesh with a rack on a movable stage, a handle threadably engaged to a threaded part formed on other end of the pinion, a friction member disposed between the stationary shaft and the handle for adjusting a couple for the handle, and a frictional force adjusting member disposed integral with the handle for adjusting a frictional force developed between the threaded part of the pinion shaft and the handle. According to the prior invention, adjusting of an intensity of couple for the handle is achieved by rotating the handle by one hand while the movable stage is retained with other hand of an operator. Specifically, since the pinion shaft is kept immovable because the movable stage is retained, the handle is displaced along the threaded part in the axial direction of the pinion shaft and a load exerted on the friction member in the direction of thrusting varies in dependence on a distance of displacement of the handle whereby a couple for the handle is adjusted.
However, the device for adjusting a couple as disclosed in the official gazette of Japanese Utility Model Publication No. 11048/1980 has such a drawback that the position of the handle relative to the couple adjusting member as seen in the axial direction should be previously adjusted prior to assembling operation, causing the device to become complicated in structure and moreover require a number of manhours for assembling and adjusting. Further, another drawbacks of the conventional device are that couple adjusting operation is performed with much difficulties because the position of the handle relative to the pinion shaft as seen in the axial direction is adjusted by rotating the threadably fitted part at which the pinion shaft is threadably fitted to the handle under the influence of a high intensity of frictional force so as to adjust the position of the handle relative to the pinion shaft as seen in the axial direction, and moreover teeth on a rack made of synthetic resin or the like material are susceptible to injury during adjusting operation.
On the other hand, the manually operable device as disclosed in the official gazette of Japanese Utility Model Publication No. 45365/1980 is so constructed that a cylindrical bearing for rotatably supporting a pinion shaft adapted to rotate together with a handle has a threaded part formed at one end thereof, a couple adjusting member adapted to be threadably engaged to the threaded part is disposed in an area located in the proximity of the handle, and the handle is displaced in the direction of thrusting by rotating the couple adjusting member so as to adjust a couple for the handle but the couple adjusting member is inhibited from rotating during rotational operation of the handle.
However, a couple adjusting unit incorporated in the last-mentioned manually operable device has a drawback that when fingers of an operator come in contact with the couple adjusting member by mistake while the handle is rotated to displace the movable stage, there is a fear that the couple adjusting member is rotated together with the handle, resulting in a couple for the hand which has been properly adjusted getting out of order.